Update to Drupal 8.6

[deviantintegral]

• Updates to Drupal 8.6.2
• Updates to the latest Selenium release.
• Splits building from tests for this project so we don't go over Circle's 40K log line limit.
• Splits each type of Drupal test into their own job (keeping kernel and unit together since they can combine for code coverage reports)
• Adds proper support for functional-js tests.

See https://github.com/deviantintegral/drupal_tests_node_example/pull/4 for an example of this (note the CS job fails because node module fails).